NMR spectrometers analyze the structures of substances by making use of resonance of atomic nuclei within a magnetic field. These NMR spectrometers have been heretofore fitted with automatic sample exchange devices to automatically and successively extract samples and to perform measurements.
FIG. 7 is a plan view of such a conventional automatic sample exchange device. FIG. 8 is a cross-sectional view taken along line VIII--VIII of FIG. 7. This exchange device comprises a support base 1, a pair of guide rails 2 mounted on the support base 1, a slidable base plate 3 mounted so as to be slidable on the support base 1 while guided by the guide rails 2, a sleeve 4 extending upright from the base plate 3, chucks 5, chuck-holding members 6 mounted on the sleeve 4, slide plates (gates) 7 capable of sliding on the chuck-holding members 6, respectively, rods 9 connected with their respective slide plates 7, springs 10 for constantly biasing the slide plates 7 to the left via the rods 9, a single-action cylinder 11 mounted to the support base 1, an x-motion cylinder 13 for moving the base plate 3 in the x-direction, and a sample rotor 15. Each slide plate 7 is provided with a hole 8 having a diameter equal to the inside diameter of the sleeve 4. The sample rotor 15 has a diameter slightly smaller than that of the hole 8. The single-action cylinder 11 has a shaft 12. Sample tubes 14 are placed in the sample rotor 15.
An x-motion auxiliary cylinder (not shown) is mounted below the x-motion cylinder 13. These x-motion cylinders including the cylinder 13 control and increase the stroke of the base plate 3 in the x-direction. The single-action cylinder 11 and its shaft 12 are designed so that when the hole 4a in the sleeve 4 registers with a sample inlet hole 1a in the body of an NMR spectrometer, the rods 9 of the chucks 5 mounted to the sleeve 4 are placed opposite to the shaft 12.
In the prior art automatic sample exchange device constructed as described above, the rod 9 of each chuck 5 is not pushed by the shaft 12 in normal state. Under this state, the biasing force of the spring 10 urges the slide plate 7 into the leftmost position (gate closed position) as viewed in the figure via the rod 9. At this leftmost position of the slide plate 7, the hole 8 is located in an eccentric relation to the hole 4a in the sleeve 4. Under this condition, if any sample tube 14 holding a sample is inserted into the holes 8 and 4a from the sample inlet hole, the bottom surface of the sample rotor 15 engages the wall defining the hole 8 in the slide plate 7. Therefore, the sample tube 14 is held in the illustrated state by the chuck 5 energized.
After holding the sample tube 14 in this way, the two x-motion cylinders including the cylinder 13 are driven to move the base plate 3 in the x-direction until the hole 4a in the sleeve 4 registers with the sample inlet hole 1a in the support base 1, whereupon the movement of the support base 1 is stopped. At this time, low-pressure air is supplied from the body of the NMR spectrometer through the sample inlet hole. The air flows through the hole 4a in the sleeve 4 and strikes the sample rotor 15.
Then, the single-action cylinder 11 is driven to push the shaft 12 forward. This shaft 12 pushes the rod 9 to the right, so that the slide plate 7 is moved to the right (gate open position). The hole 8 in the slide plate 7 is brought into registry with the hole 4a in the sleeve 4. This disengages the bottom surface of the sample rotor 15 from the wall defining the hole 8 in the slide plate 7. As a result, the sample tube 14 is released from the chuck 5, i.e., the chuck is deenergized. At this time, the rod 9 is kept pushed by the shaft 12. The sample tube 14 is kept afloat by the low-pressure air coming from below even if the chuck is deenergized. The sample tube 14 is moved downward toward the body of the NMR spectrometer by controlling the supply of the low-pressure air.
When the NMR spectrometer finishes a measurement of the sample inside the sample tube 14, air is again supplied to move the sample tube 14 toward the chuck 5. When the bottom surface of the sample rotor 15 passes beyond the slide plate 7, the single-action cylinder 11 is deactivated, thus retracting the shaft 12. The shaft 12 no longer pushes the rod 9, so that the slide plate 7 is at the leftmost position. Under this condition, the hole 8 is again placed in an eccentric relation (gate closed position) to the hole 4a in the sleeve 4. The supply of the air is stopped. The sample tube 14 is kept held by the chuck 5 energized.
In order to introduce the sample tube 14 held by an adjacent chuck 5 into the body of the NMR spectrometer, the two x-motion cylinders including the cylinder 13 are driven to shift the base plate 3 in the x-direction. The hole 4a in the sleeve 4 holding the sample tube 14 is brought into registry with the sample inlet hole 1a. Subsequently, sample tubes 14 are introduced and withdrawn in a manner similar to the foregoing processing. In this way, the sample in the body of the NMR spectrometer is automatically exchanged by the automatic sample exchange device.
In the prior art automatic sample exchange device constructed as described above, the single-action cylinder 11 for moving the slide plate 7 of the chuck is separate from the x-motion cylinder (such as 13) that carries the chuck 5 holding the sample tube 14. Therefore, these two mechanisms must be controlled separately and in an interlocking manner. Hence, complex control unit and control software are necessary.
Also, each individual tube 14 needs a separate chuck 5. Therefore, if the number of the sample tubes 14 is increased, the number of the chucks 5 is increased proportionately. This increases the cost. Furthermore, the instrument is made bulky. Moreover, since each chuck 5 grips the sample tube 14 under normal condition, the chuck is urged to release the tube only at one location. Consequently, the chuck 5 is expanded a great deal, thus requiring relatively large space. However, the space for accommodating the chucks 5 is limited and so it is difficult to increase the number of the used chucks 5 that expand a great deal as described above. Heretofore, the maximum number of used chucks as been three as shown. Accordingly, the number of the sample tubes 14 used is limited to three. It has been difficult to employ more sample tubes. Additionally, the stroke of the x-motion cylinder 13 is limited and, therefore, the base plate 3 can move only a limited distance. This also limits the number of used sample tubes 14.